The present invention relates to a method and an apparatus for correcting or compensating a cutter position for a radial deflection, in which a tire surface subjected to cutting deviates in the radial direction, and/or a lateral deflection, in which a tire surface subjected to cutting deviates in the lateral direction, in a tire grooving operation.
An apparatus for grooving in a tread surface of a new tire or a re-treaded tire has, in general, a tire supporting shaft, which supports a tire in a vertical posture, and a cutter unit, of which at least the lateral movement in the direction parallel with the tire supporting shaft and the radial movement in the direction perpendicular to the tire supporting shaft are allowed.
However, a tire itself, in general, does not have an accurate roundness, a tire tread surface is sometimes inclined to a certain degree and the tire is sometimes supported in a deviated condition and therefore, a radial distance from the center of the tire supporting shaft to the tread surface is not constant. Accordingly, radial deflection of the tread surface in the radial direction is caused. In the above situation, a tire grooving, wherein the cutter movement is controlled in accordance with a prespecified tread pattern shape by a set-up program with a tire being rotated, cannot provide constant groove depths for each tire having same size and same specification. Moreover, even if a plurality of grooves having a mutually uniform depth on the left and right sides of the tire equator are required to be formed on one tire, the depths of the grooves on the left side of the equator differ from those on the right side. Thus there is caused a problem in quality that the stability of the tire is impaired and the strength thereof is lowered.
Further, if distortion of, the tire itself and deviation in the tire supporting cause a lateral deflection of the side surface of the tire in the direction of the tire width, a tire grooving, wherein the cutter movement is controlled in accordance with a prespecified tread pattern shape by a set-up program with a tire being rotated, cannot make a groove position keep a constant relationship to the tire tread center for each tire having same size and same specification. Moreover, a deviation of the tire tread center in one tire sometimes results. Thus there is caused a problem in quality that the stability of the tire is impaired and the strength thereof is lowered.
In this connection, there has been proposed another apparatus, for example, as disclosed in Japanese Unexamined Patent Publication No. 74635/1987, wherein there is provided a non-contact type detecting means for detecting the shape of the tread surface, and the cutter position is controlled based on the detected data so that the amount of rubber being cut off from the tire is kept constant.
However, suchlike apparatus has a problem that a large frame for mounting the detecting means are required.
Further the groove depth cannot be kept constant along the entire circumferential length of the groove which is formed on the entire periphery in the circumferential direction of the tire because the cutter position in the direction of the cutting depth is kept constant only at the beginning of the cutting operation.
Moreover, an image detector is used and the cutter position in the cutting operation is determined by calculation based on the area of the tire exposed to the view of the detector in order to allow the constant amount of rubber to be cut off. However, the determination of the cutter position by calculation based on the area is very difficult particularly when the cutter acrosses another groove which has been formed already or when the radial fluctuation on the right side of the tire equator is different from that on the left side, even if the constant amount of rubber to be cut off is purposed. Since the cutter position is not movable in accordance with the radial deflection of the tire, the groove depth and the groove width cannot be kept at respective desired constant values by following the radial deflection of the tire.
Still further, since the cutter position cannot be moved in accordance with the lateral deflection of the tire, the groove position relative to the tread center cannot be kept at a desired constant value by following the lateral deflection of the tire.
An object of the present invention is to provide a method and an apparatus for grooving which provide a groove having desired constant depth and width and being formed at a desired constant position even in case that a tire has a radial deflection and/or a lateral deflection.
In accordance with the present invention, there is provided a method for compensating deflections of a tire in tire tread grooves in the tread of a tire is controlled by a plurality of operating shafts, characterized by the steps comprising moving the cutter with one of the plurality of operating shafts along a non-deflected path to cut the thread grooves in the tire, detecting deflections on the tire and, with the detected deflections, deflecting the path of movement of the cutter with another of the plurality of shafts in accordance with the detected deflection.
In accordance with the present invention, there is also provided an apparatus for compensating deflections of a tire in tire tread grooving wherein movement of a cutter for cutting tread grooves in the tread of a tire is controlled by a plurality of operating shafts comprising one shaft of the plurality of operating shafts for moving the cutter along a non-deflected path to cut the tread grooves on the tire, detecting means for detecting deflections on the tire and means connected to another shaft of the plurality of shafts and the detecting means for deflecting the cutter from the non-deflected path in accordance with the detected deflection.